Natural Agrobacterium-Mediated Transformation in the Genus Nicotiana

Agrobacterium can transfer genetic information to plants, transforming the plants naturally. An Agrobacterium plasmid fragment is transferred to the plant via bacterial infection and stably integrated into the plant’s nuclear DNA. This plasmid fragment (termed transferred DNA or T-DNA) contains several genes that are inserted into the plant’s chromosomes. Some natural plant species contain Agrobacterium T-DNA-like sequences, which have been shown to result from natural transformation. These sequences are called cellular T-DNAs or cT-DNAs. Multiple Nicotiana species have been shown to contain cT-DNA sequences and to express cT-DNA genes, qualifying these species as natural transformants. The composition and organization of the T-DNA sequences vary considerably. Sequencing the genome of the Tomentosae and Noctiflorae sections of the genus Nicotiana has identified seven cT-DNA sequences that are similar to sequences in A. rhizogenes, A. tumefaciens, and A. vitis. As some cT-DNA genes show strong growth effects when expressed in other species, they may influence the growth of the natural transformants as well. The precise mechanisms by which these genes alter growth patterns and their regulation by promoters and by plant transcription factors remain to be elucidated.